1. Field of the Invention
The present invention relates to a communication technique that utilizes multicasting in a network communication formed by a plurality of network hosts and routers such as computers, and switches, etc.
2. Description of the Related Art
The multicasting is a technique for transmitting identical information from one host to a plurality of hosts or from a plurality of hosts to a plurality of hosts, within some group. In order to realize the multicast on the Internet, a packet to which a special IP address is assigned is used, and a multicast router or switch (hereafter referred to as “routing device”) that received such a packet delivers that packet to hosts participating to that group (which will be referred to as “client hosts”). For interface between the client hosts and the routing device, a multicast control IGMP (Internet Group Management Protocol) packet separate from that for data transfer is used, and when the client host joins or leaves the multicast group, for example, the IGMP message indicating this fact is transmitted to the routing device.
However, in the conventional multicast protocol, the control information that the client hosts can receive from the routing device is very limited. For example, in the information delivery service for delivering video data, music data, etc., the accounting for the multicast data is carried out, but conventionally there is no means for notifying information regarding the accounting to the client host, and it has been difficult to know not only the accounted fee but even whether the accounting is to be carried out or not, at the client host. Also, in the case of joining to the multicast group which requires the authentication, even when the authentication fails for some reason, it has been impossible to notify that reason to the client host.